Project Summary The ability of the malaria vector mosquito Anopheles gambiae to sense and locate human blood meal hosts remains rudimentary. In this process, chemosensory signals and olfaction in particular, provide the dominant sensory inputs for Anopheline and other mosquitoes and accordingly play a critical role in modulating behaviors that impact vectorial capacity. The goal of this revised proposal is to extend ongoing preliminary studies to characterize the molecular pathways underlying the mosquito's ability to sense and respond to ammonia that is an essential component of human-derived odorants that attract blood-feeding females. Here we focus on the role of AgAmt1, a putative ammonia transporter in Anopheles gambiae that may be required for the olfactory sensory transduction of ammonia, which is a critically important, human-derived kairomone for mosquito host seeking. These studies will provide additional insights into the mechanisms of insect olfaction and constitute an important resource for the design and implementation of effective disease control strategies that target Anopheles gambiae and a wide range of related vector species.